This study consists of three projects that examine aspects of the growth and nutrition of children with sickle cell disease (SCD) and the interaction of these parameters with clinical status. Although the growth deficits of children with SCD have been previously described, the nutritional and disease related factors are poorly understood. In this study, we: Project 1: evaluate longitudinally the growth, development, nutritional status, and dietary intake of 150 SCD patients, ages birth to 18 years, and its relationship to clinical status; Project 2: assess energy balance in children (5 to 18 years old) with SCD by evaluating resting and total energy expenditure and dietary intake while in a usual state of health vs. control children; and Project 3: assess the energetic cost of acute illness by measuring the resting energy expenditure (REE) and dietary intake of children with SCD during hospitalization for an acute illness episode compared to their usual state of health.